1. Field of the Invention
The present invention relates to wireless communication encoding and decoding techniques using variable length codes, in particular to signal encoding and decoding techniques that assign different transmission times for high and low bits in the transmitted data, enabling considerable reduction in total transmission time and power saving by the data communication device.
2. Description of Related Arts
In wireless communication, data streams to be transmitted are encoded at the transmitting end, modulated into analogous waveform, and then transmitted in the form of radio frequencies or infrared beams. At the receiving end, the analogous signals are received, amplified, demodulated to digital form, and then decoded to restore the original data format.
In wireless communication, the primary objective of various coding technique is to minimize the data transmission time, and maintain signal synchronization at both ends to ensure reliable data transmission.
The wireless communication encoding and decoding techniques not only change the transmission time but also affect the power status of the data communication device. Commonly used wireless computer peripherals such as a keyboard and a mouse are connected by wireless means to maintain bidirectional communication with the host computer. Since these devices are powered by a battery, the longer it takes to transmit a data stream, the battery operation hours of the transmitting device will be further decreased. Therefore, the choice of a signal coding technique indirectly affects their power consumption and the operation time of the device.
Generally, data are transmitted in basic units called packets. Each packet is divided up into multiple segments each serving a special function in the data transmission process. A standard packet contains a preamble, a header, a control segment, a data segment, and an SFT segment, as shown in FIG. 6. Some of the more commonly used coding patterns for the data segment as shown in FIG. 7 are listed hereunder:
Non return to zero (NRL)-L coding: according to this technique, a high bit xe2x80x9c1xe2x80x9d in the data is represented by positive voltage (+V), whereas a low bit xe2x80x9c0xe2x80x9d is represented by negative voltage (xe2x88x92V).
NRZ-M coding: according to this technique, only when the bit value in a continuous bit stream changes from xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d, the voltage of the output signal is changed from the positive voltage (+V) to negative voltage (xe2x88x92V), whilst the voltage remains in the positive (+V) for all other bit conditions.
Unipolar return to zero (RZ): according to this technique, for every high bit xe2x80x9c1xe2x80x9d in the bit stream the output signal experiences one transition from negative voltage to positive voltage, and the voltage for low bit xe2x80x9c0xe2x80x9d is at the negative.
Manchester: according to this encoding and decoding technique, the signal changes once in each time unit regardless of the status of the data bit. The rising edge of the signal represents a high bit xe2x80x9c0xe2x80x9d, whilst the falling edge represents a low bit xe2x80x9c1xe2x80x9d.
Delay modulation: according to this technique, the voltage of the output signal experiences one transition in a time unit for the occurrence of each high bit xe2x80x9c1xe2x80x9d in the bit stream, by delaying the voltage transition from the preceding bit for one time unit before changing the voltage. For a low bit xe2x80x9c0xe2x80x9d, the voltage of the output signal is unchanged from the previous time unit, and for two successive low bits xe2x80x9c0xe2x80x9d, the signal voltage for the second low bit xe2x80x9c0xe2x80x9d is the inverse of the voltage for the previous bit.
In actual operation using the first three signal coding techniques the signal output does not necessarily experience voltage change in each time unit, making it more difficult to maintain signal synchronization at both ends. These techniques thereby are seldom employed in synchronous communication. The Manchester coding having the characteristics of voltage transition in each time unit naturally is better for synchronous transmission with wireless means. However, in the Manchester coding every bit of information is assigned the same length of time, that means a fixed length code is used in the transmission data. The difference in transmission time between a variable length code and a fixed length code is cumulative for larger amounts of transmission data, resulting in much longer transmission time than that using variable length codes.
For example, as shown in FIG. 8, using the Manchester coding technique, the bit stream 01100011xe2x80x9401011110 represents two data bytes (2 bytes=16 bits). The encoded signals at the transmitting end show that every bit in these two bytes is occupied by the same number of time units (2T in this embodiment), thus the total transmission time for these two bytes is 16xc3x972T=32T. Longer transmission time using the Manchester coding also consumes more electric power in the data communication process.
The present invention is to address the above mentioned problem with variable length codes.
The main object of the present invention is to provide wireless communication encoding and decoding techniques using variable length codes, wherein a low bit xe2x80x9c0xe2x80x9d and a high bit xe2x80x9c1xe2x80x9d in the data stream are differentiated by different transmission time, thus enabling reduction in the total transmission time and power saving by the data communication device.
The second object of the invention is to provide wireless communication encoding and decoding techniques using variable length codes, wherein every bit of transmitted data is accompanied by a voltage transition in the output signal, and the signal synchronization at both ends of the communication link ensures high reliability in data transmission.
The wireless communication encoding and decoding techniques using the variable length codes comprise the steps of:
defining a time unit (T);
defining the number of time units (N) to be assigned for representing the high bit xe2x80x9c1xe2x80x9d, for example 2T; and
defining the number of time units (M) to be assigned for representing the low bit xe2x80x9c0xe2x80x9d, for example 1T;
wherein two adjacent data bits are to be represented by different voltages in the signal output.
The features and structure of the present invention will be more clearly understood when taken in conjunction with the accompanying figures.